Mine broke too. Fix is easy
Depending on how bad it is, it could be easier than you think! I broke one of mine off too. Take the pulley completely off so there is no "load" or stress on the bolts. Then there should be some bit of bolt left that you can grab with either your fingers or a small needle nose pliers or needle nose vise grips. Carefully turn the bolt to loosen. I would also get some kind of lubricant to spray on the bolt to allow the least amount of friction in the threads. Mine came right out no problem. I replaced them with SS metric socket heads. I think they were a DIN 912 M5x12. Good luck.